The Fukushima Daiichi nuclear disaster was a catastrophic failure at the Fukushima Daiichi Nuclear Power Plants on 11 March 2011. The nuclear power plant was located on a 3.5-square-kilometre site in the towns of Okuma and Futaba in the Futaba District of Fukushima Prefecture, Japan. There were altogether 10 nuclear reactors, with 5 reactors using old designs and the rest using new designs.
All the Fukushima plants, including the newer plants, were all based on General Electric(GE) designs. A lucrative contracts had been made between General Electric and Tokyo Electric Power Co (Tepco) to service the GE nuclear plants in Japan. General Electric is an American multinational ...view middle of the document...
Hence, from no.6 to no.10 nuclear reactors, Mark II design was used. With Mark II design, the reactor buildings are large enough to accommodate the backup generators. The last 4 reactors that started building at Fukushima Daini complex about seven miles away in the late 1970s also further improved its design on Mark II, and had better protection against earthquakes and tsunamis.
Over the years, Japanese governement had tightened the standards for earthquake preparedness a few times and updated the plants. The older reactors with Mark I design were rated Class B for a lower earthquake-preparedness rating while the new reactors with Mark II design were graded Class S. According to the interviews after the Fukushima nuclear disaster, the Tepco's top engineers that guided the company's nuclear division were all well aware of the inconsistent placement of the diesel generators at Fukushima Daiichi between reactor No.6 and the older reactors 1 through 5. However, they didn't point out the vulnerable Mark I design and didn't made retrofitting or improvements to the older designs. It is believed that the engineers didn't point out the needs of upgrading the old reactors to newer designs was because of the high costs associated with backfitting old reactors with new designs. In addition, during that time, Tepco was criticized and pressured by the citizens for having high electricity rates and such a high costs of backfitting the old reactors would have been difficult.
In 1998, there were new regulatory requirements for the nuclear plants. Tepco decided to provide at least two backup generators to each of the reactors at Fukushima Daiichi. New backup generators were placed in a building located higher on a mountainside. All 6 units were given access to these generators. Eventhough this was a major safety improvement, the switching stations which is called "meta-kura" that sent power from the backup generators to the cooling system were still in poor protection, while switching station of No.6 was already inside the reactor building. If the switching station failed, the generators would not be able to generate electricity for the cooling system.
In 2001, the Fukushima Daiichi's No.1 reactor renewed its original 30-year operating permit and it received 10-year extension. In 2011, five weeks before the nuclear disaster, another 10-year extension was obtained again. The older reactors were flawed, but the regulators never reviewed if the old design passed the current safety standards.
When the tsunami hit Fukushima Daiichi on 11 March, it knocked out the power grid and destroyed the generators located in the turbine buildings. On the other hand, the three generators that provided at the mountainside functioned well, however, the meta-kura at reactors No.1 to 4 that sent the electricity to the cooling system got swamped and failed. The radioactive fuel at reactors No.1 to 3 began overheating and melt. The meltdown of the reactors no.1 through 3 causing...